Lipase-catalyzed acidolysis of tristearin with oleic or caprylic acids to produce structured lipids

Two different structured lipids (SL) were synthesized by transesterifying tristearin with caprylic acid (C8:0) or oleic acid (C18:1). The objective was to synthesize SL containing stearic acid (C18:0) at the sn-2 position as possible nutritional and low-calorie fats-The reaction was catalyzed by IM60 lipase from Rhizomucor miehei in the presence of n-hexane. The effects of reaction parameters affecting the incorporation of caprylic acid into tristearin were compared with those for incorporating oleic acid into tristearin. For all parameters studied, oleic acid incorporation was higher than caprylic acid. The range of conditions favorable for synthesizing high yields of C8:0-containing SL was narrower than for oleic acid. An incubation time of 12-24 h and an enzyme content of 5% (w/w total substrates) favored C8:0 incorporation. The mole percentage of incorporated C18:1 did not increase further at enzyme additions greater than 10%. C18:1 incorporation decreased with the addition of more than 10% water (w/w total substrates) to the tristearin-oleic acid reaction mixture. Increasing the mole ratio of fatty acid (FA) to triacylglycerol increased oleic acid incorporation. The highest C8:0 incorporation was obtained at a 1:6 mole ratio of tristearin to FA. Positional analysis confirmed that C18:0 remained at the sn-2 position of the synthesized SL. The melting profiles of tristearin-caprylic acid and tristearin-oleic acid SL displayed peaks between -20 to 30 degrees C and -20 to 40 degrees C, respectively. Their solid fat contents (similar to 25%) at 25 degrees C suggest possible use in spreads or for inclusion with other fats in specialized blends.